The present invention relates to a motor comprising: a stator constituted by a base plate, a circuit board and a stator core having magnetic poles radially outwardly extended therefrom; and an outer rotor, which is rotatably provided to the base plate and which has rotor magnets facing the stator magnetic poles.
Motors have been used for rotating recording media, e.g., flexible disks, optical disks, cassette tapes. Motors having outer rotors are preferably used for rotating recording media because they can stably rotate at fixed speed. For example, a motor having an outer rotor is disclosed in Japanese Patent Gazette No. 11-32466. In the motor, a stator core is provided on one face of a base plate, and a flexible circuit board is adhered on the other face. The outer rotor is rotatably provided to the base plate with a bearing member. The stator core has a plurality of tooth sections, which are radially outwardly extended and on which coils are winded so as to form stator magnetic poles. The outer rotor has rotor magnets, which face the stator magnetic poles. To make the motor small, the base plate has opening sections (accommodating sections), which correspond to the tooth sections of the stator core. Each of the coils is partially accommodated in the opening section, so that the motor can be thinner.
However, in the small motor, capacity of a driving circuit is limited, and temperature must be restricted. Further, motor characteristics, especially characteristics of torque must be improved. To improve characteristics of torque, the stator core including the tooth sections must be thicker, so that diameters of the coils must be greater. Therefore, sizes of the opening sections of the base plate must be greater, too. If the sizes of the opening sections are made greater, the base plate must be weak. Further, area of the flexible circuit board, which is adhered on the base plate, must be small, so that it must be difficult to wire and mount parts, e.g., Hall element, in such small spaces.